U.S. patent application number 13/509020 was filed with the patent office on 2012-10-04 for radio communication system, self-optimizing system, radio base station, and radio parameter setting method.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Yoshinori Watanabe.
Application Number | 20120252440 13/509020 |
Document ID | / |
Family ID | 43991478 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120252440 |
Kind Code |
A1 |
Watanabe; Yoshinori |
October 4, 2012 |
RADIO COMMUNICATION SYSTEM, SELF-OPTIMIZING SYSTEM, RADIO BASE
STATION, AND RADIO PARAMETER SETTING METHOD
Abstract
The present invention provides a self-optimizing system for
setting a radio parameter on a radio base station that manages a
cell, including an update value calculation section that calculates
an update value of a determining factor of the radio parameter
based on traffic statistics information and on radio channel
quality information that indicates radio channel quality of the
cell and of a specific neighbor cell of the neighbor cells, a
reliability evaluation section that evaluates reliability of the
calculated update value of the determining factor, an update
determination section that determines whether or not to apply the
update value of the factor to the radio base station, and a radio
parameter updating section that sets the radio parameter determined
by the update value of the factor on the radio base station when
the update value of the factor is determined to be applied to the
radio base station.
Inventors: |
Watanabe; Yoshinori;
(Minato-ku, JP) |
Assignee: |
NEC CORPORATION
Tokyo
JP
|
Family ID: |
43991478 |
Appl. No.: |
13/509020 |
Filed: |
September 15, 2010 |
PCT Filed: |
September 15, 2010 |
PCT NO: |
PCT/JP2010/065899 |
371 Date: |
May 10, 2012 |
Current U.S.
Class: |
455/423 ;
455/422.1; 455/436 |
Current CPC
Class: |
H04W 24/04 20130101;
H04W 24/02 20130101 |
Class at
Publication: |
455/423 ;
455/422.1; 455/436 |
International
Class: |
H04W 24/00 20090101
H04W024/00; H04W 36/30 20090101 H04W036/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2009 |
JP |
2009-258055 |
Claims
1. A radio communication system comprising: a radio base station
that manages a cell, mobile terminals that are connected to the
cell and measures radio channel quality of the cell and radio
channel quality of specific neighbor cells of neighbor cells that
are in the vicinity of the cell, and a parameter setting unit that
sets a radio parameter on said radio base station, wherein said
parameter setting unit comprises: an update value calculation
section that calculates an update value of a determining factor of
the radio parameter based on communication traffic statistics
information of the cell and the neighbor cells and on radio channel
quality information that indicates radio channel quality measured
by said mobile terminals; a reliability evaluation section that
evaluates the reliability of the update value of the factor
calculated by said update value calculation section; an update
determination section that determines whether or not to apply the
update value of the factor to said radio base station, based on the
evaluation result by said reliability evaluation section; and a
radio parameter updating section that sets the radio parameter
determined by the update value of the factor in said radio base
station when a determination is made that the update value of the
factor is to be applied to said radio base station.
2. The radio communication system according to claim 1, wherein the
radio channel quality information includes at least one from among
a received power of pilot signals transmitted from the cell and the
neighbor cells and a signal-to-interference ratio of pilot signals
transmitted from the cell and the neighbor cells.
3. The radio communication system according to claim 1, wherein
said reliability evaluation section calculates the reliability of
the update value of the factor as an output of an evaluation
function that inputs the number of mobile terminals connected to
the cell or the number of reports of the radio channel quality
information received from the mobile terminals.
4. The radio communication system according to claim 3, wherein the
number of mobile terminals connected to the cell, said number being
inputted to the evaluation function, is defined by a coverage area
that represents a geographical scope of the cell while the number
of reports of the radio channel quality information, said reports
being sent from said mobile terminals and said number being
inputted to the evaluation function, are defined by an overlap area
of the coverage of the cell and the coverage of the neighbor
cells.
5. The radio communication system according to claim 1, wherein
said parameter setting unit further comprises an initial value
calculation section that calculates an initial value of the
factor.
6. The radio communication system according to claim 5, wherein
said initial value calculation section calculates the initial value
of the factor based on radio base station information including at
least an installation position of said radio base station.
7. The radio communication system according to claim 5, wherein
said reliability evaluation section calculates the reliability of
the initial value of the factor as an output of an evaluation
function that inputs the overlap area of the coverage of the cell
and the coverage of the neighbor cells.
8. The radio communication system according to claim 7, wherein
said update determination section determines whether or not to
apply the update value to said radio base station based on a
magnitude relationship between the reliability of the initial value
of the factor and the reliability of the update value of the
factor.
9. The radio communication system according to claim 8, wherein
when it is determined not to apply the update value of the factor
to said radio base station, said radio parameter updating section
determines the radio parameter based on the initial value of the
factor.
10. The radio communication system according to claim 9, wherein
said radio parameter updating section performs a predetermined
computation on the reliability of the initial value of the factor
and the reliability of the update value of the factor and
designates a calculated value as reliability of the value to be
applied to said radio base station, where either the initial value
or the update value is applied, and the other is not applied, to
said radio base station.
11. The radio communication system according to claim 1, wherein:
as each of said mobile terminals moves, said mobile terminal
performs a handover to change a connected radio cell; and the
communication traffic statistics information includes at least one
from among the number of handover attempts, the number of handover
failures, and the number of handover failures classified by failure
causes, where the handover attempts are made by said mobile
terminals connected to the cell to perform handovers to the
neighbor cells serving as handover destinations.
12. The radio communication system according to claim 11, wherein
the radio parameter is a neighbor cell list that indicates the
specific neighbor cell.
13. The radio communication system according to claim 12, further
comprising a surrounding base station that manages a surrounding
cell located around the cell, wherein the factor is a neighbor
relationship between the cell and the surrounding cell.
14. The radio communication system according to claim 13, wherein
said radio parameter updating section extracts the neighbor cells
based on update values of the neighbor relationship and registers a
predetermined number of neighbor cells with the neighbor cell list
in descending order of reliability of the update values of the
neighbor relationship between the extracted neighbor cells and the
cell.
15. The radio communication system according to claim 13, wherein
said radio parameter updating section extracts the neighbor cells
based on initial values and update values of the neighbor
relationship and registers a predetermined number of neighbor cells
with the neighbor cell list in descending order of reliability of
the initial values or update values of the neighbor relationship
between the extracted neighbor cells and the cell.
16. The radio communication system according to claim 11, wherein
the radio parameter is a threshold for differences between a value
that represents the radio channel quality of the cell and values
that represent the radio channel quality of the neighbor cells; and
when the difference between the value that represents the radio
channel quality of the cell and the value that represents the radio
channel quality of any of the neighbor cells exceeds the threshold,
said radio base station makes said mobile terminals report the
radio channel quality of the cell and the radio channel quality of
the neighbor cell.
17. The radio communication system according to claim 16, wherein
the factors are a first offset value that represents the radio
channel quality of the cell and a second offset value that
represents the radio channel quality of the specific neighbor
cell.
18. The radio communication system according to claim 17, wherein
said update value calculation section classifies the handover
failure causes into first failure causes that can be remedied by
updating the first offset value and second failure causes that can
be remedied by updating the second offset value, tabulates the
total number of handover failures separately for the first and
second failure causes, and calculates an update value of either the
first or second offset values based on a magnitude relationship
between the total number of handover failures due to the first and
second failure causes.
19. The radio communication system according to claim 17, wherein
said update value calculation section calculates a handover failure
rate for each of the neighbor cells based on the number of handover
attempts and the number of handover failures, evaluates unevenness
in the calculated handover failure rate among the neighbor cells,
and determines based on a result of the evaluation whether to
calculate the second offset value for all of the neighbor cells in
common or calculate the second offset value separately for each of
the neighbor cells.
20. The radio communication system according to claim 19, wherein
said update value calculation section quantifies the degree of
unevenness in the failure rate among the neighbor cells using a
Herfindahl index or entropy and evaluates the unevenness in the
handover failure rate among the neighbor cells based on the
quantified degree of unevenness in the failure rate among the
neighbor cells.
21. (canceled)
22. A parameter setting apparatus for setting a radio parameter on
a radio base station that manages a cell, comprising: an update
value calculation section that calculates an update value of a
determining factor of the radio parameter based on traffic
statistics information of the cell and neighbor cells that are in
the vicinity of the cell and on radio channel quality information
that indicates radio channel quality of the cell and radio channel
quality of specific neighbor cell of the neighbor cells, where the
radio channel quality is measured by mobile terminals connected to
the cell; a reliability evaluation section that evaluates
reliability of the update value of the factor calculated by said
update value calculation section; an update determination section
that determines whether or not to apply the update value of the
factor to said radio base station, based on an evaluation result by
said reliability evaluation section; and a radio parameter updating
section that sets the radio parameter determined by the update
value of the factor in said radio base station when a determination
is made that the update value of the factor is to be applied to
said radio base station.
23. A radio base station for managing a cell and setting a radio
parameter of the radio base station, comprising: an update value
calculation section that calculates an update value of a
determining factor of the radio parameter based on traffic
statistics information of the cell and neighbor cells that are in
the vicinity of the cell and on radio channel quality information
that indicates radio channel quality of the cell and radio channel
quality of specific neighbor cell of the neighbor cells, where the
radio channel quality is measured by mobile terminals connected to
the cell; a reliability evaluation section that evaluates
reliability of the update value of the factor calculated by said
update value calculation section; an update determination section
that determines whether or not to apply the update value of the
factor to the radio base station, based on an evaluation result by
said reliability evaluation section; and a radio parameter updating
section that sets the radio parameter determined by the update
value of the factor in the radio base station when a determination
is made that the update value of the factor is to be applied to
said radio base station.
24. A radio parameter setting method that is applied to a parameter
setting apparatus for setting a radio parameter on a radio base
station that manages a cell, the radio parameter setting method
comprising: calculating an update value of a determining factor of
the radio parameter based on traffic statistics information of the
cell and neighbor cells that are in the vicinity of the cell and on
radio channel quality information that indicates radio channel
quality of the cell and radio channel quality of specific neighbor
cell of the neighbor cells, where the radio channel quality is
measured by mobile terminals connected to the cell; evaluating
reliability of the calculated update value of the determining
factor; determining whether or not to apply the update value of the
factor to said radio base station, based on an evaluation result;
and setting the radio parameter determined by the update value of
the factor on said radio base station when a determination is made
that the update value of the factor is to be applied to said radio
base station.
Description
TECHNICAL FIELD
[0001] The present invention relates to a radio communication
system, a self-optimizing system, a radio base station, and a radio
parameter setting method that set radio parameters on a radio base
station.
BACKGROUND ART
[0002] Generally, a radio communication system has mobile terminals
10, radio base stations 30, and mobile communication core network
50 as shown in FIG. 1.
[0003] Mobile terminal 10 transmits and receives data such as
communication traffic and control traffic to and from radio base
station 30.
[0004] Radio base station 30 transmits and receives data to and
from mobile terminals 10 and mobile communication core network 50
connected through wired links 40. Around radio base station 30,
radio cell 35 is arranged as an effective range in which mobile
terminals 10 each have radio link 20 with radio base station 30.
Radio base station 30 manages radio cell 35 arranged in its own
periphery, whereas mobile terminal 10 establishes a connection with
radio cell 35 that radio base station 30 manages and transmits and
receives data to and from radio base station 30.
[0005] Mobile communication core network 50 is composed of an
exchanger and a server machine (not shown) and is connected to
radio base stations 30 through respective wired links 40 and is
connected to external network 70 through wired link 60 so as to
transmit and receive data to and from radio base stations 30 and
external network 70.
[0006] In such a radio communication system, radio parameters of
radio base station 30 need to be appropriately set up so as to
satisfy predetermined communication qualities in all the service
areas in which services are provided. Examples of such radio
parameters are total transmission powers of radio base stations 30,
tilt angles on the vertical and horizontal planes of a radio base
station antenna, a neighbor cell list, and a handover
threshold.
[0007] In the following description, it is assumed that as radio
parameters, a neighbor cell list and a handover threshold are set
on radio base station 30.
[0008] First, the neighbor cell list will be described.
[0009] In the radio communication system, radio cells are arranged
on the plane of all the service area so as to provide services.
[0010] When mobile terminal 10 moves from the connected radio cell
to another radio cell (neighbor cell), mobile terminal 10 performs
a so-called handover, which is a process that switches the
connected radio cell to another radio cell. In this process, mobile
terminal 10 is pre-instructed to report measured radio channel
quality of the connected radio cell and the neighbor cells to radio
base station 30 that manages the connected radio cell if the radio
channel quality of the connected radio cell deteriorates. When the
radio channel quality is reported from mobile terminal 10 to radio
base station 30, radio base station 30 determines a handover
destination radio cell.
[0011] To reduce the load imposed on mobile terminal 10 and process
the handover quickly, a method that measures the radio channel
quality of only the connected radio cell of mobile terminal 10 and
the neighbor cells to which neighbor the cell mobile terminal 10
establishes a connection is generally used. The neighbor cell list
shows radio cells whose radio channel quality is to be measured and
reported by mobile terminals 10 placed under control of radio base
station 30. The neighbor cell list is generated when a
communication carrier registers radio cells to each radio cell, and
the neighbor cell list is reported to mobile terminals 10 by radio
base station 30 through a downlink channel.
[0012] Radio base station 30 determines a handover destination
radio cell from the radio cells whose radio channel quality has
been reported by mobile terminal 10. Therefore, mobile terminal 10
cannot perform a handover to radio cells whose radio channel
qualities have not been reported to radio base station 30 by mobile
terminal 10. Consequently, if radio cells have been omitted from
the neighbor cell list, since mobile terminal 10 cannot perform a
handover to an appropriate radio cell, a call may be abnormally
terminated or a handover to an inappropriate radio cell may result
in deterioration of communication qualities. Thus, it is important
to generate a neighbor cell list in which radio cells have not been
omitted so as to ensure good communication qualities.
[0013] On the other hand, an upper limit of the number of radio
cells that can be registered to a neighbor cell list has been set
up so as to reduce the load imposed on a channel through which the
neighbor cell list is reported and in order to reduce the load
imposed on mobile terminal 10 that needs to measure radio channel
qualities of radio cells and report them to radio base station 30.
Thus, it is necessary to preferentially register radio cells that
are likely to contribute to an improvement of communication
qualities to the neighbor cell list so as to register major radio
cells to the neighbor cell list.
[0014] Next, the handover threshold will be described.
[0015] Generally, when a deterioration in radio channel quality of
a connected radio cell is reported from mobile terminal 10 to radio
base station 30, the condition for determining the presence or
absence of a trigger is given by Expression (1).
[Mathematical expression 1]
P.sub.s+O.sub.s<P.sub.t+O.sub.t (1)
where Ps and Pt are received powers of pilot signals transmitted
from radio base station 30 that manages a connected radio cell and
radio base station 30 that manages a neighbor cell, respectively.
Os and Ot are offset values of received powers where Os is applied
to the received power of the pilot signal transmitted from radio
base station 30 that manages the connected radio cell, whereas Ot
is applied to the received power of the pilot signal transmitted
from neighbor base station 30. Ot may be set to a value that
differs in each neighbor cell.
[0016] Expression (1) is rephrased to Expression (2)
[ Mathematical expression 2 ] { P t - P s > Th HO Th HO = O s -
O t ( 2 ) ##EQU00001##
the parameter Th.sub.HO may be referred to as a handover
determination threshold (handover threshold). The handover
threshold is used by mobile terminal 10 to determine whether to
report the radio channel quality of the connected radio cell and
neighbor cell. A larger difference between the radio channel
quality of the connected radio cell and the radio channel quality
of the neighbor cell than the handover threshold triggers reporting
the radio channel quality.
[0017] If the handover threshold is not set appropriately, there
may be a delay in the timing for mobile terminal 10 to report the
radio channel quality. Consequently, mobile terminal 10 may fail to
report the radio channel quality of a handover candidate neighbor
cell to radio base station 30 before mobile terminal 10 reaches the
position at which a handover is needed. This could cause a delay in
performing a handover, resulting in abnormal disconnection of
communication. Also, there can be a case where a neighbor cell
whose radio channel quality has increased temporarily is determined
to be a handover candidate and radio channel quality of the
neighbor cell declines right after handover to the neighbor cell,
resulting in an abnormal disconnection of communication. Therefore,
in order to ensure high communication quality, how to set the
handover threshold that will enable a handover to be performed at
an appropriate position, by adjusting a determining factor, such as
offset values Os and Ot, of a radio parameter is important.
[0018] Specific example of a method for setting radio parameters
will be described below.
[0019] As a method for setting radio parameters, a method (first
method) that uses a radio area design tool (design tool) is
generally known.
[0020] FIG. 2 is a diagram for illustrating a method for generating
a neighbor cell list that is set as a radio parameter by the first
method.
[0021] Referring to FIG. 2, to generate a neighbor cell list of
radio cell 35A (Cell A) managed by radio base station 30A, the
first method extracts radio base stations 30B and 30C located
within a certain distance range from radio base station 30A. Then,
the first method calculates overlap areas of the coverage
(geographical scopes of radio cells 35) of radio cells 35B (Cell B)
and 35C (Cell C) managed, respectively, by radio base stations 30B
and 30C and the coverage of radio cell 35A.
[0022] In FIG. 2, the coverage of radio cell 35A and the coverage
of radio cell 35B overlap each other (overlap area S), and
consequently radio cell 35B is regarded as a neighbor cell of radio
cell 35A. On the other hand, the coverage of radio cell 35A and the
coverage of radio cell 35C do not overlap each other, and
consequently radio cell 35C is not regarded as a neighbor cell of
radio cell 35A.
[0023] Then, the neighbor cells of radio cell 35A are registered in
a neighbor cell list in descending order of the overlap area up to
an upper limit of the number of radio cells that can be registered
to the neighbor cell list. The resulting neighbor cell list is
provided in radio base station 30A.
[0024] The overlap area of coverage can be calculated by a coverage
estimation function of the design tool.
[0025] In an area design stage, the handover threshold that is set
as a radio parameter by the first method has the same value for all
the radio cells in a service area.
[0026] In this way, the first method can set the neighbor cell list
and the handover threshold as radio parameters.
[0027] However, the neighbor cell list and the handover threshold
set by the first method may have defects.
[0028] FIG. 3 is a diagram for illustrating a problem with the
method for generating a neighbor cell list by the first method.
[0029] When coverage 351A and coverage 351B of radio cell 35A (Cell
A) managed by radio base station 30A and radio cell 35B (Cell B)
managed by radio base station 30B are estimated in first method,
estimated coverage 352A and estimated coverage 352B may be smaller
than real coverage 351A and real coverage 351B due to estimation
errors. Consequently, even when real coverage 351A and real
coverage 351B have overlap area 353 to some degree, if estimated
coverage 352A and estimated coverage 352B do not overlap, radio
cells 35A and 35B are not regarded as neighbor cells that are in
the vicinity of each other, resulting in an omission from
registration in the neighbor cell list.
[0030] Also, FIG. 4 is a diagram for illustrating a problem with a
handover threshold that is set by the first method.
[0031] In FIG. 4, mobile terminal 10 (not shown) connected to radio
cell 35B attempts a handover to radio cell 35A. In this case, if
the handover threshold is set to a fixed value as with the first
method, when overlap area 353 of coverage of radio cell 35A and
coverage of radio cell 35B managed, respectively, by radio base
stations 30A and 30B are small, handover position 321 can be
located outside overlap area 353. Then, the handover will be
performed too early, resulting in an abnormal disconnection of
communication.
[0032] Also, depending on the set value of the handover threshold,
the handover will be performed too late. In such a case,
communication will be disconnected abnormally as well.
[0033] In this way, the neighbor cell list and the handover
threshold set as radio parameters by the first method may have
defects.
[0034] To deal with defects of the radio parameters set by the
first method, the radio parameters need to be corrected as
appropriate after the area design if any defects are revealed by
field testing.
[0035] Thus, in recent years, as disclosed in Non Patent Literature
1 and Non Patent Literature 2, an autonomous system that
autonomously optimizes radio parameters has been under
consideration.
[0036] FIG. 5 is a schematic diagram showing an example of a
structure of a radio communication system that is provided with a
self-optimizing system.
[0037] The radio communication system shown in FIG. 5 has mobile
terminals 10, radio base stations 30, mobile communication core
network 50, and self-optimizing system 90. In FIG. 5, similar
components to those in FIG. 1 are denoted by similar reference
numeral and their description will be omitted in the following.
[0038] Self-optimizing system 90 is connected to radio base
stations 30 through wired links 80 and to mobile communication core
network 50 through wired link 85. Self-optimizing system 90
controls an exchanger and a server machine in mobile communication
core network 50 as well as radio base station 30.
[0039] Non Patent Literature 1 describes a method (second method)
for autonomously optimizing and updating a neighbor cell list to be
set as a radio parameter in a radio communication system provided
with a self-optimizing system.
[0040] FIG. 6 is a schematic diagram for illustrating a method for
generating a neighbor cell list by the second method.
[0041] The self-optimizing system described in Non Patent
Literature 1 tabulates the number of handover attempts (a) to each
radio cell (Listed Cell) registered in the neighbor cell list, as a
handover destination. In addition, the self-optimizing system
described in Non Patent Literature 1 tabulates the number of
reports (n) from mobile terminals stating that the received power
of a pilot signal is equal to or higher than a threshold regarding
each radio cell (Detected Cell) unregistered in the neighbor cell
list.
[0042] Based on the tabulated results, the self-optimizing system
described in Non Patent Literature 1 registers a predetermined
number of radio cells in which the number of reports (n) is equal
to or larger than a threshold in the neighbor cell list out of the
Detected Cells in descending order of the number of reports (n),
and removes the Listed Cells in which the number of attempts (a) is
a small proportion, i.e., a proportion equal to or smaller than a
threshold in the total number of attempts of all the neighbor
cells, from the existing neighbor cell list, and thereby updates
the neighbor cell list that is a radio parameter.
RELATED ART LITERATURE
[0043] Non Patent Literature 1: D. Soldani, "Self-optimizing
Neighbor Cell List for UTRA FDD Networks Using Detected Set
Reporting", pp. 694-pp. 698, IEEE VTC2007. [0044] Non Patent
Literature 2: 3GPP TR 36.902 v1.2.0: "Radio Access Network
(E-UTRAN); Self-configuring and self-optimizing network use cases
and solutions"
DISCLOSURE OF THE INVENTION
[0045] However, with the second method, if a radio cell connected
with a small number of mobile terminals has an uneven geographical
or temporal distribution of mobile terminals, the radio parameters
set on the radio base station that manages the radio cell may get
updated based on local or temporary actual measurement information.
In such a case, there is a problem in that even if the radio
parameters are updated based on local or temporary actual
measurement information, the distribution of mobile terminals often
varies greatly before and after the update, which may result in a
failure to improve the communication quality.
[0046] To avoid this problem it is reasonable not to update the
radio parameters until the total number of mobile terminals
connected to the radio cell or the number of reports from mobile
terminals are increased, but this method has a problem in that
deterioration of communication quality due to defects in the set
values of the radio parameters can become prolonged.
[0047] An object of the present invention is to provide a radio
communication system, self-optimizing system, radio base station,
and radio parameter setting method that can solve the problems
described above.
[0048] To accomplish the foregoing object, the present invention
provides a first radio communication system comprising: a radio
base station that manages a cell, mobile terminals that are
connected to the cell and measures radio channel quality of the
cell and radio channel quality of specific neighbor cells of
neighbor cells that are in the vicinity of the cell, and a
self-optimizing system that sets a radio parameter on the radio
base station, wherein the self-optimizing system comprises: an
update value calculation section that calculates an update value of
a determining factor of the radio parameter based on communication
traffic statistics information of the cell and the neighbor cells
and on radio channel quality information that indicates radio
channel quality measured by the mobile terminals; a reliability
evaluation section that evaluates the reliability of the update
value of the factor calculated by the update value calculation
section; an update determination section that determines whether or
not to apply the update value of the factor to the radio base
station, based on the evaluation result by the reliability
evaluation section; and a radio parameter updating section that
sets the radio parameter determined by the update value of the
factor in the radio base station when a determination is made that
the update value of the factor is to be applied to said radio base
station.
[0049] To accomplish the foregoing object, the present invention
provides a second radio communication system comprising: a radio
base station that manages a cell, mobile terminals that are
connected to the cell and measure radio channel quality of the cell
and radio channel quality of specific neighbor cells of neighbor
cells that are in the vicinity of the cell, and a self-optimizing
system that sets a radio parameter on the radio base station,
wherein the self-optimizing system comprises: an initial value
calculation section that calculates an initial value of a
determining factor of the radio parameter; an update value
calculation section that calculates an update value of the factor
based on communication traffic statistics information of the cell
and the neighbor cells and on radio channel quality information
that indicates radio channel quality measured by the mobile
terminals; a reliability evaluation section that evaluates
reliability of the initial value of the factor calculated by the
initial value calculation section and reliability of the update
value of the factor calculated by the update value calculation
section; an update determination section that determines applying a
weighted average value of the initial value and update value of the
factor calculated using the reliability of the initial value and
update value of the factor evaluated by the reliability evaluation
section to the radio base station; and a radio parameter updating
section that sets the radio parameter determined by the weighted
average value on the radio base station when a determination is
made that the weighted average value is to be applied to said radio
base station.
[0050] To accomplish the foregoing object, the present invention
provides a self-optimizing system for setting a radio parameter on
a radio base station that manages a cell, comprising: an update
value calculation section that calculates an update value of a
determining factor of the radio parameter based on traffic
statistics information of the cell and neighbor cells that are in
the vicinity of the cell and on radio channel quality information
that indicates radio channel quality of the cell and radio channel
quality of specific neighbor cell of the neighbor cells, where the
radio channel quality is measured by mobile terminals connected to
the cell; a reliability evaluation section that evaluates
reliability of the update value of the factor calculated by the
update value calculation section; an update determination section
that determines whether or not to apply the update value of the
factor to the radio base station, based on an evaluation result by
the reliability evaluation section; and a radio parameter updating
section that sets the radio parameter determined by the update
value of the factor in the radio base station when a determination
is made that the update value of the factor is to be applied to
said radio base station.
[0051] To accomplish the foregoing object, the present invention
provides a radio base station for managing a cell and setting a
radio parameter of the radio base station itself, comprising: an
update value calculation section that calculates an update value of
a determining factor of the radio parameter based on traffic
statistics information of the cell and neighbor cells that are in
the vicinity of the cell and on radio channel quality information
that indicates radio channel quality of the cell and radio channel
quality of specific neighbor cell of the neighbor cells, where the
radio channel quality is measured by mobile terminals connected to
the cell; a reliability evaluation section that evaluates
reliability of the update value of the factor calculated by the
update value calculation section; an update determination section
that determines whether or not to apply the update value of the
factor to the radio base station itself, based on an evaluation
result by the reliability evaluation section; and a radio parameter
updating section that sets the radio parameter determined by the
update value of the factor in the radio base station itself when a
determination is made that the update value of the factor is to be
applied to said radio base station.
[0052] To accomplish the foregoing object, the present invention
provides a radio parameter setting method that is applied to a
self-optimizing system for setting a radio parameter on a radio
base station that manages a cell, the radio parameter setting
method comprising: calculating an update value of a determining
factor of the radio parameter based on traffic statistics
information of the cell and neighbor cells that are in the vicinity
of the cell and on radio channel quality information that indicates
radio channel quality of the cell and radio channel quality of
specific neighbor cell of the neighbor cells, where the radio
channel quality is measured by mobile terminals connected to the
cell; evaluating reliability of the calculated update value of the
determining factor; determining whether or not to apply the update
value of the factor to the radio base station, based on an
evaluation result; and setting the radio parameter determined by
the update value of the factor on the radio base station when a
determination is made that the update value of the factor is to be
applied to said radio base station.
[0053] According to the present invention, the self-optimizing
system calculates an update value of a determining factor of the
radio parameter based on traffic statistics information of the cell
managed by the radio base station and neighbor cells that are in
the vicinity of the cell and on radio channel quality information
that indicates radio channel quality of the cell and specific
neighbor cell of the neighbor cells, the radio channel quality
being measured by a mobile terminal connected to the cell,
determines whether or not to apply the update value of the factor
to the radio base station, based on the evaluation result of the
reliability of the calculated update value of the factor; and sets
the radio parameter determined by the update value of the factor on
the radio base station when the update value of the factor is
determined to be applied.
[0054] Thus, even when the geographical distribution of mobile
terminals connected to the cell is uneven, since whether or not to
apply the update value of the factor to the radio base station can
be determined based on the evaluation result of the reliability of
the update value of the factor, it is possible to reduce the
likelihood that the communication quality may not be improved even
if the radio parameter is updated.
[0055] Also, since whether or not to apply the update value of the
factor to the radio base station can be determined based on the
evaluation result of the reliability of the calculated update value
of the factor, there is no need to wait until the number of mobile
terminals connected to the cell or the number of reports from
mobile terminals exceed a predetermined value, and thus
deficiencies of the initial value of the radio parameter can be
remedied quickly, thereby preventing prolonged deterioration of
communication quality.
BRIEF DESCRIPTION OF DRAWINGS
[0056] FIG. 1 is a schematic diagram showing an example of a
structure of a typical radio communication system.
[0057] FIG. 2 is a schematic diagram illustrating a method for
generating a neighbor cell list by a first method.
[0058] FIG. 3 is a schematic diagram illustrating a problem with
the method for generating a neighbor cell list by the first
method.
[0059] FIG. 4 is a schematic diagram illustrating a problem with a
handover threshold that is set by the first method.
[0060] FIG. 5 is a schematic diagram showing an example of a
structure of a radio communication system that is provided with a
self-optimizing system.
[0061] FIG. 6 is a schematic diagram illustrating a method for
generating a neighbor cell list by a second method.
[0062] FIG. 7 is a block diagram showing a structure of a
self-optimizing system according to a first exemplary
embodiment.
[0063] FIG. 8 is a flowchart illustrating an operation of the
self-optimizing system shown in FIG. 7.
[0064] FIG. 9 is a schematic diagram showing an example of
management information managed by an update value calculation
section shown in FIG. 7.
[0065] FIG. 10 is a flowchart illustrating an operation of the
update value calculation section shown in FIG. 7.
[0066] FIG. 11A is a schematic diagram showing an example of an
evaluation function used by a reliability evaluation section shown
in FIG. 7 to evaluate reliability of an update value of a neighbor
relationship when the update value of the neighbor relationship is
"neighbor."
[0067] FIG. 11B is a schematic diagram showing a function used to
determine a threshold for the number of reports needed to return
reliability 1 in FIG. 11A.
[0068] FIG. 11C is a schematic diagram showing an example of an
evaluation function used by the reliability evaluation section
shown in FIG. 7 to evaluate reliability of an update value of the
neighbor relationship when the update value of the neighbor
relationship is "non-neighbor."
[0069] FIG. 11D is a schematic diagram showing a function used to
determine a threshold for the number of reports needed to return
reliability 1 in FIG. 11C.
[0070] FIG. 12 is a schematic diagram showing an example of
management information managed by an update determination section
shown in FIG. 7.
[0071] FIG. 13 is a schematic diagram showing an example of
management information managed by the update determination section
shown in FIG. 7.
[0072] FIG. 14 is a block diagram showing a structure of a
self-optimizing system according to a second exemplary
embodiment.
[0073] FIG. 15 is a flowchart illustrating an operation of the
self-optimizing system shown in FIG. 14.
[0074] FIG. 16A is a schematic diagram showing an example of an
evaluation function used by a reliability evaluation section shown
in FIG. 14 to evaluate reliability of an initial value of a
neighbor relationship.
[0075] FIG. 16B is a schematic diagram showing an example of an
evaluation function used by the reliability evaluation section
shown in FIG. 14 to evaluate reliability of an initial value of an
offset value.
[0076] FIG. 17 is a schematic diagram showing an example of
management information managed by an update determination section
shown in FIG. 14.
[0077] FIG. 18 is a schematic diagram showing an example of
management information managed by the update determination section
shown in FIG. 14.
[0078] FIG. 19 is a schematic diagram showing an example of
management information managed by the update determination section
shown in FIG. 14.
[0079] FIG. 20 is a schematic diagram showing an example of
management information managed by the update determination section
shown in FIG. 14.
[0080] FIG. 21 is a schematic diagram showing an example of
management information managed by an update determination section
of a self-optimizing system according to a third exemplary
embodiment.
EXEMPLARY EMBODIMENTS
[0081] Next, with reference to the accompanying drawings, exemplary
embodiments will be described.
[0082] In the following, an example in which a self-optimizing
system in the radio communication system according to the present
invention shown in FIG. 5 sets radio parameters on radio base
station 30 will be described. Thus, similar components to those
shown in FIG. 2 are denoted by similar reference numerals and their
description will be omitted in the following.
[0083] The present invention is not limited to the radio
communication system shown in FIG. 5. Instead, without departing
from the spirit of the present invention, the present invention may
be applied to a radio communication system that is provided with a
radio base station control device arranged between mobile
communication core network 50 and radio base station 30 and also
applied to a radio communication system where the function of the
self-optimizing system is incorporated in a radio based station
control device or radio base station 30. In addition, the present
invention may be also applied to the case in which a radio base
station management device is arranged between the self-optimizing
system and radio base station 30.
[0084] Besides, hereinafter the term "radio parameter(s)" is used
to mean the neighbor cell list or the handover threshold or both.
The neighbor cell list is determined using a neighbor relationship
between radio cells as a factor while the handover threshold is
determined using an offset value in Expression (1) as a factor. In
this way, since the neighbor relationship and the offset value are
determining factors of radio parameters, description will be given
below mainly of how to determine the neighbor relationship between
radio cells and how to determine the offset value in Expression
(1). Incidentally, although in the example described below, the
neighbor relationship (neighbor or non-neighbor) between radio
cells and the offset value in Expression (1) are managed by the
self-optimizing system, these factors may be managed inside the
radio base station control apparatus or radio base station 30.
First Exemplary Embodiment
[0085] FIG. 7 is a schematic diagram showing a structure of
self-optimizing system 100 according to a first exemplary
embodiment of the present invention.
[0086] Self-optimizing system 100 shown in FIG. 7 has base station
information storage section 101, initial value calculation section
102, measurement information storage section 103, communication
statistics storage section 104, quality deterioration detection
section 105, update value calculation section 106, reliability
evaluation section 107, update determination section 108, and radio
parameter updating section 109.
[0087] Base station information storage section 101 is a region
that stores radio base station information about radio area design.
Specific examples of the radio base station information include
information about the installation position of radio base station
30 and total transmit power of radio base station 30, gain and
installation direction of a radio base station antenna, and
features around radio base station 30 such as geography, building
structure, and building layout.
[0088] Initial value calculation section 102 acquires radio base
station information about a radio cell managed by radio base
station 30 from base station information storage section 101 and
calculates the initial value of a determining factor of a radio
parameter.
[0089] Measurement information storage section 103 is a region that
stores measurement information of radio channel quality measured by
mobile terminals 10 connected to a radio cell managed by radio base
station 30. Specific examples of measurement information of radio
channel quality include information of received powers of pilot
signals transmitted from a connected radio cell and neighbor cells
measured by each mobile terminal 10 and the signal-to-interference
ratio between the pilot signal transmitted from the connected radio
cell and the neighbor cells.
[0090] Communication statistics storage section 104 is a region
that stores communication traffic statistics information with
respect to the operating radio communication system, where the
communication traffic is measured by radio base stations 30.
Specific examples of traffic statistics information include
statistics of individual radio cell such as the number of handover
attempts to each radio cell serving as a handover destination cell
or the number of handover failures classified by cause of failure.
Incidentally, the number of handover failures classified by cause
of failure can be counted by identifying cause of failure such as
premature handovers or belated handovers based on communication
history information on mobile terminals 10, for example, using the
method described in Non Patent Literature 2.
[0091] Quality deterioration detection section 105 computes factors
such as handover failure rate based on the traffic statistic
information stored in communication statistic storage section 101,
thereby detects any radio cell whose radio channel quality has
deteriorated, and designates the detected radio cell as a cell to
be optimized. The radio parameter is updated for radio base station
30 that manages the radio cell designated as a cell to be
optimized.
[0092] Update value calculation section 106 calculates an update
value of a factor for the cell to be optimized based on the
measurement information of radio channel quality of the cell to be
optimized and the traffic statistics information about the cell to
be optimized, where the measurement information is acquired from
measurement information storage section 103 and the traffic
statistics information is acquired from communication statistics
storage section 104.
[0093] Reliability evaluation section 107 evaluates the reliability
of the factor's update value calculated by update value calculation
section 106. Reliability evaluation section 107 acquires the
measurement information of radio channel quality and the traffic
statistics information used in calculating the update value from
update value calculation section 106 and evaluates the reliability
of the update value by means of an evaluation function specific to
each radio cell using the acquired information as an input.
[0094] Update determination section 108 determines whether or not
to actually apply the update value of the factor to radio base
station 30 based on an evaluation result by reliability evaluation
section 107 concerning the reliability of the factor's update
value.
[0095] When update determination section 108 makes a determination
that the update value of the factor is to be applied to radio base
station 30, radio parameter updating section 109 determines a radio
parameter based on the factor's update value and sets the radio
parameter on radio base station 30.
[0096] Next, operation of self-optimizing system 100 will be
described.
[0097] FIG. 8 is a flowchart illustrating the operation of
self-optimizing system 100.
[0098] Initial value calculation section 102 calculates an initial
value of each factor for the radio cell managed by each radio base
station 30. Radio parameter updating section 109 determines an
initial value of the radio parameter based on the calculated
initial value of the factor (at step S100). Then, radio parameter
updating section 109 sets the initial value of the radio parameter
on radio base station 30 (at step S101).
[0099] In step S100, the initial value of the factor can be
calculated by the first method. For example, the initial value of a
neighbor relationship between radio cells can be calculated by
identifying a neighbor cell based on overlap areas of the coverage
of a cell and the coverage of radio cells around the radio cell.
Alternatively, the initial value can be calculated by selecting
radio base stations 30 close to radio base station 30 that manages
the radio cell in order of increasing distance and then by
regarding the radio cells managed by selected radio base stations
30 as neighbor cells.
[0100] On the other hand, regarding the offset value, the same
initial value can be used across the entire radio communication
system.
[0101] Also, according to this exemplary embodiment, the
determining the initial values of the radio parameters in step S100
is not essential, and if step S100 is omitted, an empty neighbor
cell list that does not contain any neighbor cell and a handover
threshold set to a fixed value are provided in radio base stations
30 as radio parameters.
[0102] Quality deterioration detection section 105 acquires traffic
statistic information from communication statistic storage section
104 and detects radio cells whose radio channel quality has
deteriorated (at step S102). Specifically, quality deterioration
detection section 105 computes handover failure rates of each radio
cell based on the number of handover attempts and the number of
handover failures and detects any radio cell whose handover failure
rate is equal to or higher than a predetermined threshold as a
radio cell whose radio channel quality has deteriorated. In the
following, the detected radio cell is designated as a cell to be
optimized.
[0103] When a cell to be optimized is detected (at step S102: YES),
update value calculation section 106 calculates an update value of
the factor for the cell to be optimized based on the measurement
information of radio channel quality and the traffic statistics
information (at step S103).
[0104] Reliability evaluation section 107 evaluates the reliability
(R) of the factor's update value calculated by update value
calculation section 106 (at step S104). Details of the reliability
calculation method will be described later with reference to FIG.
11. When reliability R is larger than the threshold (Th), update
determination section 108 makes a determination to apply the update
value of the factor to radio base station 30 (at step S105).
[0105] Once update determination section 108 makes a determination
that the update value of the factor is to be applied to radio base
station 30, radio parameter updating section 109 determines a radio
parameter based on the update value of the factor and sets the
radio parameter on radio base station 30 to update the radio
parameter (at step S106).
[0106] Self-optimizing system 100 detects any radio cell that has
degraded radio channel quality (at step S102) even after the radio
parameter is updated. If the radio channel quality of any radio
cell satisfies a required level as a result of the radio parameter
update, radio base station 30 that manages the radio cell is
removed from a list of radio base stations 30 subject to radio
parameter update. On the other hand, when the radio channel quality
of the radio cell does not satisfy the required level,
self-optimizing system 100 performs the process starting with
calculating an update value of the factor and proceeding to
updating the radio parameter again (steps S103 to S106).
Self-optimizing system 100 repeats updating the radio parameter
until the radio channel quality satisfies the required level or
until the cumulative amount of change in the radio parameter
exceeds a predetermined threshold. Self-optimizing system 100
finishes the overall process when there is no longer any radio cell
that needs adjustment of the radio parameter.
[0107] Next, an operation performed by update value calculation
section 106 to calculate an update value of a factor will be
described.
[0108] When the factor is a neighbor relationship between radio
cells, update value calculation section 106 can calculate the
update value of the neighbor relationship using the second
method.
[0109] On the other hand, when the factor is an offset value,
update value calculation section 106 can calculate the update value
by acquiring traffic statistics information from communication
statistics storage section 104. Now, a method for calculating the
update value of the offset value will be described in more detail
with reference to FIG. 9 and FIG. 10.
[0110] FIG. 9 is a diagram showing an example of management
information managed when update value calculation section 106
calculates the update value of the offset value.
[0111] For each neighbor cell, update value calculation section 106
manages communication statistics of handovers performed from a cell
to be optimized (source cell) to the neighbor cell (target cell)
serving as a handover destination. Specifically, regarding
handovers from a source cell to target cell i serving as a handover
destination, update value calculation section 106 manages the
number of handover attempts (a.sub.i), the number of failures
(f.sub.i), and the number of failures (c.sub.ij) classified by
cause of failure c.sub.j.
[0112] FIG. 10 is a flowchart illustrating an operation performed
by update value calculation section 106 to calculate the update
value of the offset value.
[0113] Update value calculation section 106 calculates a handover
failure rate of each target cell based on the number of handover
attempts (a.sub.i) and failures (f.sub.i) acquired from
communication statistics storage section 104 (at step S200).
Furthermore, update value calculation section 106 evaluates the
presence or absence of unevenness in the failure rate among the
target cells (at step S201).
[0114] The presence or absence of unevenness in the failure rate
among the target cells can be evaluated, for example, by using the
H index (Herfindahl index) given by Expression (3), which
quantifies the concentration ratio of a failure rate distribution
among the target cells.
[ Mathematical expression 3 ] { H = i = 1 M h i h i = ( p i j = 1 M
p j ) 2 ( 3 ) ##EQU00002##
[0115] Where i is an identifier of the target cell, M is the total
number of target cells, p, is the failure rate of handovers from
the source cell to target cell i serving as a handover destination.
A value range of the H index is 1/M to 1. The higher the failure
rate with respect to a specific target cell, the closer the value
is to 1 while the more uniform the rate of failure distribution
over all the target cells, the closer the value is to 1/M.
[0116] Update value calculation section 106 determines that the
rate of failure distribution over the target cells is significantly
uneven and that handover failures are concentrated on some target
cells, for example, when the H index is equal to or larger than a
predetermined threshold (Rx), and otherwise, update value
calculation section 106 determines that handover failures occur
with respect to unspecific target cells (at step S202).
Incidentally, although in the example described in this exemplary
embodiment, the Herfindahl index is used to quantify unevenness,
another index, such as entropy, may be used for quantifying of
unevenness.
[0117] If it is determined at step S202 that there is unevenness in
the failure rate among the target cells, update value calculation
section 106 selects each target cell that is in the vicinity of the
source cell (at step S203) and evaluates failure rate values with
respect to the target cell (at step S205) by referring to the
failure rate calculated at step S200 (at step S204).
[0118] If the failure rate R.sub.HOFail(i) with respect to target
cell i is equal to or lower than a threshold (Th.sub.HOFail) (at
step S205: NO), update value calculation section 106 uses the
current offset value as an update value (at step S206). On the
other hand, if the failure rate R.sub.HOFail(i) is higher than the
threshold (Th.sub.HOFail) (at step S205: YES), update value
calculation section 106 tabulates the number of handover failures
f.sub.i with respect to target cell i separately by failure causes
c.sub.j (at step S207). Specifically, update value calculation
section 106 classifies causes of handover failure c.sub.j into
causes (C.sub.INC) that can be remedied if the offset value is
increased and causes (C.sub.DEC) that can be remedied if the offset
value is decreased. Furthermore, regarding handover attempts from
the source cell to target cell i serving as a handover destination,
based on the number of handover failures c.sub.ij classified by
causes of failure c.sub.j, update value calculation section 106
calculates the total number of failures F.sub.INC(i) caused by
C.sub.INC as well as the total number of failures F.sub.DEC(i)
caused by C.sub.DEC using Expression (4).
[ Mathematical expression 4 ] { F INC ( i ) = c j .di-elect cons. C
INC c ij F DEC ( i ) = c j .di-elect cons. C DEC c ij ( 4 )
##EQU00003##
[0119] Update value calculation section 106 evaluates the values of
F.sub.INC(i) and F.sub.DEC(i) (at steps S208 and S210). If
F.sub.INC(i) is larger than F.sub.DEC(i) by a hysteresis value
(Th.sub.hyst) or more, update value calculation section 106
provides the update value obtained by adding a fixed value
(.DELTA.x) to the current offset value as an offset value to be
applied only to target cell i (at step SS09). On the other hand, if
F.sub.DEC(i) is larger than F.sub.INC(i) by the hysteresis value
(Th.sub.hyst) or more, update value calculation section 106
provides the update value obtained by subtracting the fixed value
(.DELTA.x) from the current offset value as an offset value to be
applied only to target cell i (at step S211). If there isn't any
difference that is comparable to the hysteresis value (Th.sub.hyst)
between F.sub.DEC(i) and F.sub.INC(i), the current offset value is
used as an update value (at step S206).
[0120] Update value calculation section 106 performs the process of
steps S203 to S211 in relation to all the target cells that are in
the vicinity of the source cell (at step S212).
[0121] On the other hand, if it is determined at step S202 that
there is no unevenness in the failure rate among the target cells,
update value calculation section 106 calculates the overall failure
rate of the source cell (at step S213) and evaluates the value of
the failure rate (at step S214).
[0122] If the overall failure rate R.sub.HOFail of the source cell
is equal to or lower than the threshold (Th.sub.HOFail) (at step
S214: NO), update value calculation section 106 sets the current
offset value as an update value (at step S215). On the other hand,
if failure rate R.sub.HOFail is higher than the threshold
Th.sub.HOFail (at step S214: YES), update value calculation section
106 tabulates the number of failures f.sub.i with respect to target
cell i separately by causes of failure c.sub.j (at step S216).
[0123] Specifically, as in the case of step S207, update value
calculation section 106 classifies causes of handover failure
c.sub.j into causes (C.sub.INC) that can be remedied if the offset
value is increased and causes (C.sub.DEC) that can be remedied if
the offset value is decreased. Furthermore, update value
calculation section 106 calculates the total number of failures
F.sub.INC caused by C.sub.INC as well as the total number of
failures F.sub.DEC caused by C.sub.DEC using Expression (5).
[ Mathematical expression 5 ] { F INC = i c j .di-elect cons. C INC
c ij F DEC = i s j .di-elect cons. C DEC c ij ( 5 )
##EQU00004##
[0124] Update value calculation section 106 evaluates the values of
F.sub.INC and F.sub.DEC (at steps S217 and S219). If F.sub.INC is
larger than F.sub.DEC by the hysteresis value (Th.sub.hyst) or
more, update value calculation section 106 provides the update
value obtained by adding a fixed value (.DELTA.x) to the current
offset value as an offset value to be applied to all the target
cells that are in the vicinity of the source cell (at step S218).
On the other hand, if F.sub.DEC is larger than F.sub.INC by the
hysteresis value (Th.sub.hyst) or more, update value calculation
section 106 provides the value obtained by subtracting the fixed
value (.DELTA.x) from the current offset value as an offset value
to be applied to all the target cells that are in the vicinity of
the source cell (at step S220). If there isn't any difference that
is comparable to the hysteresis value (Th.sub.hyst) between
F.sub.DEC and F.sub.INC, the current offset value is used as an
update value (at step S215).
[0125] FIG. 11A and FIG. 11C are diagrams showing examples of an
evaluation function used by reliability evaluation section 107 to
evaluate the reliability of a factor's update value. The evaluation
function is a function for an update value of a neighbor
relationship between radio cells and has the property of returning
higher reliability as the number of reports from mobile terminals
10 connected to the radio cell per unit area or the number of
mobile terminals 10 increases.
[0126] FIG. 11A is an evaluation function of reliability in the
case where the update value of the neighbor relationship is
"neighbor," showing a relationship between the reliability (R) of
the update value and the number of reports (n.sub.i) from mobile
terminals 10 connected to the source cell stating that the received
power of pilot signals transmitted from target cell i is equal or
higher than a threshold. FIG. 11B is a function used to determine a
threshold (Th.sub.n) for the number of reports needed to return 1
as reliability in FIG. 11A. The function has the property of
returning a higher value of the threshold (Th.sub.n) as an overlap
area (s.sub.i) of the coverage of the source cell and coverage of
target cell i increases. The overlap area of the coverage of the
source cell and coverage of target cell i can be calculated using a
design tool as in the case of the first method.
[0127] FIG. 11C is an evaluation function in the case where the
update value of the neighbor relationship is "non-neighbor,"
showing a relationship between the reliability (R) of the update
value and the number of mobile terminals 10 (m) connected to the
source cell. FIG. 11D is a function used to determine a threshold
(Th.sub.m) for the number of reports needed to return 1 as
reliability 1 in FIG. 11C. The function has the property of
returning a higher value of the threshold (Th.sub.m) as a coverage
area (s) of the source cell increases. The coverage area can be
calculated using a design tool as in the case of the first
method.
[0128] Evaluation functions for the update value of the neighbor
relationship between radio cells have been shown in FIG. 11A and
FIG. 11C, and similar evaluation functions can be used for an
update value of the offset value. That is, when the update value is
an offset value applied to specific target cell i, the reliability
of the update value can be evaluated by defining evaluation
functions similar to those shown in FIG. 11A and FIG. 11B for the
number of failures of handovers from the source cell to target cell
i serving as a handover destination and the overlap area of
(s.sub.i) of the coverage of the source cell and the coverage of
target cell i. Incidentally, if the update value is a value
obtained by increasing the current offset value, the reliability of
F.sub.INC(i) can be evaluated as the number of handover failures,
and if the update value is a value obtained by decreasing the
current offset value, the reliability of F.sub.DEC(i) can be
evaluated.
[0129] When the update value is an offset value to be applied to
all the target cells that are in the vicinity of the source cell,
the reliability of the update value can be evaluated by defining
evaluation functions similar to those shown in FIG. 11A and FIG.
11B for the sum total of handover failures with respect to
individual target cells serving as handover destinations and the
sum total (S') of the overlap areas of the coverage of the source
cell and the coverage of individual target cells. Incidentally, if
the update value is a value obtained by increasing the current
offset value, the reliability of F.sub.INC can be evaluated as the
number of handover failures, and if the update value is a value
obtained by decreasing the current offset value, the reliability of
F.sub.DEC can be evaluated.
[0130] FIG. 12 is a diagram showing an example of management
information managed by update determination section 108 when the
factor is a neighbor relationship between radio cells.
[0131] Referring to FIG. 12, the initial value of the neighbor
relationship, the update value and the reliability of the update
value, and the neighbor relationship setting applied to radio base
station 30 and the reliability of the neighbor relationship setting
are managed as management information for each neighbor cell
(target cell). As the neighbor relationship setting, the update
value is adopted when the reliability of the update value is larger
than the threshold (Th). Otherwise, the initial value is adopted.
Incidentally, in FIG. 12, the threshold (Th) for reliability is
0.4. When the initial value is adopted, the reliability of the
setting is set equal to the threshold (Th).
[0132] First, radio parameter updating section 109 extracts target
cells whose neighbor relationship setting is "neighbor" from the
management information managed by update determination section 108,
in descending order of reliability until the upper limit number of
cells that can be registered to the neighbor cell list is reached.
Then, radio parameter updating section 109 registers the extracted
target cells to the neighbor cell list and sets the resulting
neighbor cell list on radio base station 30.
[0133] FIG. 13 is a diagram showing an example of management
information managed by update determination section 108 when the
factor is an offset value applied to a specific target cell.
[0134] Referring to FIG. 13, the initial value of the offset value,
the update value and the reliability of the update value, and the
offset value setting to radio base station 30 are managed as
management information for each neighbor cell (target cell). As the
offset value setting, the update value is adopted when the
reliability of the update value is larger than the threshold (Th).
Otherwise, the initial value is adopted. When the initial value is
adopted, the reliability of the setting is set equal to the
threshold.
[0135] Radio parameter updating section 109 sets the offset value
setting of each target cell managed by update determination section
108 on radio base station 30.
[0136] In this way, according to this exemplary embodiment,
self-optimizing system 100 calculates update values of the
determining factors of radio parameters to be set on radio base
station 30 that manages a cell to be optimized and evaluates the
reliability of the update values based on the number of mobile
terminals 10 connected to the cell to be optimized, the number of
reports of radio channel quality from mobile terminals 10, overlap
areas of the coverage of the cell to be optimized and the coverage
of neighbor cells, and the coverage area of the cell to be
optimized. Then, self-optimizing system 100 determines a radio
parameter based on whether the evaluated reliability of the
factor's update value exceeds a predetermined threshold and sets
the radio parameter on radio base station 30.
[0137] Consequently, even if there is unevenness in the
geographical or temporal distribution of mobile terminals 10
connected to the cell to be optimized since it can be determined
whether or not to apply the update value to radio base station 30
according to the reliability of the factor's update value
calculated based on actual measurement information about mobile
terminals 10, it is possible to reduce the likelihood that the
communication quality may not be improved even if the radio
parameter is updated.
[0138] Also, there is no need to wait until the number of mobile
terminals 10 connected to the cell to be optimized or the number of
reports from mobile terminals 10 exceeds a predetermined number and
deficiencies of the initial value of the radio parameter can be
remedied quickly, thereby preventing prolonged deterioration of
communication quality.
[0139] Incidentally, according to this exemplary embodiment, an
example in which the radio communication system is provided with
self-optimizing system 100 as well as radio base stations 30 and in
which the self-optimizing system 100 sets radio parameters on radio
base stations 30 is provided was presented. However, the present
invention is not limited such an example. Alternatively, radio base
station 30 may set radio parameters with which radio base station
itself is provided.
[0140] The traffic statistics information used to calculate the
update value of the factor is collected by radio base station 30
and radio channel quality information is reported from mobile
terminals 10 to radio base station 30. Thus, radio base station 30
can calculate the update value of the factor based on such
information. Also, if evaluation functions and the like used to
evaluate calculated update values of factors are stored in radio
base station 30, radio base station 30 can evaluate the reliability
of update values of the factors and determine whether or not to
apply the update values of the factors to radio base station
30.
Second Exemplary Embodiment
[0141] Self-optimizing system 200 according to a second exemplary
embodiment evaluates the reliability of a factor's initial value,
as well, and applies the factor's initial value or update value,
whichever has the higher reliability, to radio base station 30. The
same components and operation steps as those in the first exemplary
embodiment are denoted by the same reference numerals/step numbers
as the corresponding components/operation steps in the first
exemplary embodiment, and description thereof will be omitted and
mainly differences will be described below.
[0142] FIG. 14 is a diagram showing a configuration of
self-optimizing system 200 according to the second exemplary
embodiment.
[0143] Self-optimizing system 200 according to this exemplary
embodiment is different from self-optimizing system 100 according
to the first exemplary embodiment in that initial value calculation
section 102 is substituted with initial value calculation section
202, in that reliability evaluation section 107 is substituted with
reliability evaluation section 207, and in that update
determination section is substituted with update determination
section 208.
[0144] Initial value calculation section 202 calculates an initial
value of each factor based on radio base station information
acquired from base station information storage section 101 and
outputs the calculated initial value of the factor to reliability
evaluation section 207.
[0145] In addition to evaluations similar to those according to the
first exemplary embodiment, reliability evaluation section 207
performs a reliability evaluation of the factor's initial value
calculated by initial value calculation section 202 as well.
Reliability evaluation section 207 acquires radio base station
information used for initial value calculations from base station
information storage section 101 and calculates the reliability of
the initial value using an evaluation function specific to each
radio cell and using the acquired information as an input.
[0146] Update determination section 208 compares reliability
between the factor's initial value and update value, the
reliability having been evaluated by reliability evaluation section
207, and determines whether to apply the factor's update value
calculated by update value calculation section 106 to radio base
station 30.
[0147] Next, operation of self-optimizing system 200 will be
described.
[0148] FIG. 15 is a flowchart illustrating the operation of
self-optimizing system 200.
[0149] Steps S100 to S103 are the same as the first exemplary
embodiment described above, and thus description thereof will be
omitted.
[0150] Reliability evaluation section 207 evaluates the reliability
(R) of the update value calculated by update value calculation
section 106 (at step S104). Furthermore, reliability evaluation
section 207 also evaluates reliability (R.sub.0) of the initial
value calculated by initial value calculation section 202 (at step
S110).
[0151] Update determination section 208 compares reliability R of
the update value with reliability R.sub.0 of the initial value (at
step S111). When reliability R of the update value is higher than
reliability R.sub.0 of the initial value, update determination
section 208 determines to apply the update value to radio base
station 30. When reliability R.sub.0 of the initial value is equal
to or higher than reliability R of the update value, update
determination section 208 determines to apply the initial value to
radio base station 30. Incidentally, priority may be given to the
initial value or the update value by adding a weighting factor w to
a decision criterion as shown by Expression (6):
[Mathematical expression 6]
wR>R.sub.0 (6)
[0152] After update determination section 108 makes a selection,
based on the initial value or update value, as to which radio
parameter is to be applied to radio base station 30, radio
parameter updating section 109 sets the selected radio parameter on
radio base station 30, and thereby updates the radio parameter (at
step S106).
[0153] Self-optimizing system 200 detects any radio cell with
degraded radio channel quality (at step S102) even after the radio
parameter is updated. If the radio channel quality of any radio
cell satisfies a required level as a result of the radio parameter
update, radio base station 30 that manages the radio cell is
removed from a list of radio base stations 30 subject to radio
parameter update. On the other hand, when the radio channel quality
of the radio cell does not satisfy the required level,
self-optimizing system 100 performs the process of calculating an
update value of the factor and updating the radio parameter again
(steps S103 to S106 and steps S110 to S111). Self-optimizing system
200 repeats updating the radio parameter until the radio channel
quality satisfies the required level or a cumulative amount of
change in the radio parameter exceeds a predetermined threshold.
Self-optimizing system 100 finishes the overall process when there
is no longer any radio cell that needs adjustment of the radio
parameter.
[0154] FIG. 16A and FIG. 16B are diagrams showing examples of an
evaluation function used by reliability evaluation section 207 to
evaluate reliability of an initial value.
[0155] FIG. 16A is an evaluation function for an initial value of a
neighbor relationship, showing the relationship of the reliability
(R.sub.0) of the initial value to overlap area (s.sub.i) of the
coverage of the source cell and thus coverage of target cell i. The
initial value of the neighbor relationship calculated by the first
method has the property of having high accuracy when the overlap
area (s.sub.i) is significantly large or small and reduced accuracy
when the overlap area (s.sub.i) is not significantly large or small
due to coverage estimation errors. To allow for this property, the
reliability evaluation function has the property of returning low
reliability when the overlap area (si) is between a threshold
(Th.sub.small) and threshold (Th.sub.Large) and otherwise returning
high reliability.
[0156] FIG. 16B is an evaluation function for an initial value of
an offset value, showing a relationship of reliability (R.sub.0) of
the initial value to overlap area (s.sub.i) of the coverage of the
source cell and the coverage of target cell i. A handover position
needs to be in an overlap part of the coverage of the source cell
and the coverage of target cell i. Therefore, the larger the
overlap area (s.sub.i), the larger the design margin, increasing
the likelihood that the handover position that depends on the
offset value set to a fixed value will fall within the overlap part
of the coverage of the source cell and the coverage of target cell
i. To allow for this property, the reliability evaluation function
has the property of returning high reliability as the overlap area
(s.sub.i) increases.
[0157] FIG. 17 is a diagram showing an example of management
information managed by update determination section 208 when the
factor is a neighbor relationship between radio cells. FIG. 18 is a
diagram showing an example of management information managed by
update determination section 208 when the factor is an offset
value.
[0158] Referring to FIG. 17 and FIG. 18, the management information
according to this exemplary embodiment is different from the
management information shown in FIG. 12 and FIG. 13 in that the
reliability of the initial value is included in the management
information. Regarding the setting applied to radio base station
30, the initial value or update value of the factor, whichever has
the higher reliability, is adopted. Regarding the reliability of
the setting, the higher of the reliabilities of the initial value
and update value is used as shown FIG. 17 and FIG. 18.
[0159] Regarding the reliability of the setting, the sum or
difference of the reliabilities of the initial value and the update
value may be used alternatively, where either initial value or the
update value is applied, and the other is not applied, to radio
base station 30. For example, the reliability (R') of the setting
can be calculated from the reliability of the initial value
(R.sub.0), the reliability (R) of the update value, and a weighting
factor (w) using Expression (7):
[Mathematical expression 7]
R'=|R.sub.0+wR| (7)
[0160] In so doing, the sum (0<w) of the reliabilities is used
when the initial value and the update value are equal to each
other, and the difference (w<0) of the reliabilities is used
when the initial value and the update value are different from each
other. Regarding the reliability of the update value, the
difference of the reliabilities is used similarly by calculating
the difference between the reliability of the value adopted as the
update value and the reliability of the value not adopted as the
update value. Examples of management information managed by update
determination section 108 when the sum or difference of the
reliabilities is used are shown in FIG. 19 and FIG. 20.
[0161] FIG. 19 is a diagram showing an example of management
information managed by update determination section 208 when the
factor is a neighbor relationship between radio cells. FIG. 20 is a
diagram showing an example of management information managed by
update determination section 208 when the factor is an offset
value.
[0162] In this way, according to the this exemplary embodiment,
self-optimizing system 200 also evaluates the reliability of the
factor's initial value and applies the factor's initial value or
update value, whichever has the higher reliability, to radio base
station 30.
[0163] According to the first exemplary embodiment, the initial
value is not updated until the reliability of the update value
exceeds the threshold. In contrast, according to the this exemplary
embodiment, since the initial value of the factor is updated
immediately if the reliability of the initial value of the factor
is lower than the update value, deficiencies of the initial value
can be remedied more quickly.
Third Exemplary Embodiment
[0164] Self-optimizing system 300 according to a third exemplary
embodiment applies a weighted average value of the factor's initial
value and update value to radio base station 30 by calculating the
weighted average value according to the respective reliabilities of
the initial value and update value. The same components and
operation steps as those in the second exemplary embodiment are
denoted by the same reference numerals/step numbers as the
corresponding components/operation steps in the second exemplary
embodiment, and description thereof will be omitted and mainly
differences will be described below.
[0165] Self-optimizing system 300 according to this exemplary
embodiment is different from self-optimizing system 200 according
to the second exemplary embodiment only in that update
determination section 208 is replaced by update determination
section 308.
[0166] Update determination section 308 applies a weighted average
value of a factor's initial value and update value to radio base
station 30 by calculating the weighted average value according to
the respective reliabilities of the initial value and update
value.
[0167] Next, operation of update determination section 308 will be
described.
[0168] FIG. 21 is a diagram showing an example of management
information managed by update determination section 308 when the
factor is an offset value.
[0169] Referring to FIG. 21, instead of selecting a setting to be
applied to radio base station 30 from the initial value and update
value of the offset value, update determination section 308 obtains
the setting to be applied to radio base station 30 by calculating a
weighted average value of the initial value and update value
according to the respective reliabilities of the initial value and
update value using Expression (8):
[ Mathematical expression 8 ] O ' = R O + R 0 O 0 R + R 0 ( 8 )
##EQU00005##
[0170] where O.sub.0 and O are the initial value and update value
of the offset value, respectively; O' is the setting to be applied
to radio base station 30; and R.sub.0 and R are reliabilities of
the initial value and update value of the offset value,
respectively.
[0171] In this way, according to the third exemplary embodiment,
the self-optimizing system applies a weighted average value of the
factor's initial value and update value to radio base station 30 by
calculating the weighted average value according to the respective
reliabilities of the initial value and update value.
[0172] According to the second exemplary embodiment, since one of
the factor's initial value and update value is applied to radio
base station 30, if there is a large difference between initial
value and update value, conditions of the radio communication
system can vary greatly before and after an update of the radio
parameter, resulting in instability. In contrast, according to this
exemplary embodiment, in which the radio parameter using a weighted
average of the factor's initial value and update value gradually
changes, the stability of the radio communication system when the
radio parameter is updated is increased.
[0173] While the invention has been particularly shown and
described with reference to exemplary embodiments thereof, the
invention is not limited to these exemplary embodiments. It will be
understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the claims.
[0174] The present application is based upon and claims the benefit
of priority from Japanese patent application No. 2009-258055, filed
on Nov. 11, 2009, the disclosure of which is incorporated herein in
its entirety by reference.
* * * * *